Steels_ Metallurgy and Applications, Third Edition

Low-carbon structural steels 145

1200

1050

9OO

J~

e~

| 750

IR r

600

450

9 0 0

iFerrlte + "~,~

. ~eajdlte ** ~.
~:i -
700 800

eop ~o

~'. \

"o 9 9

9 9

• Martensites 1.. Balnltes
  ....... t I I I
  300 400 500 600
  Transformation temperature (~

Figure 2.5 Relationship between 50% transformation temperature and tensile strength
(After Pickering 3)

promote hardenability but there may also be a need to include elements such as
vanadium to improve tempering resistance.

Structure-property relationships in ferrite-pearlite steels

Following the derivation of the Hall-Petch relationship:

1

~y = ~ + kyd-~

it was proposed that this basic equation for yield strength could be extended to
take account of the strengthening effects of alloying elements. Thus:

1

try = ~ + k' (% alloy) + kyd-~

During the late 1950s and early 1960s, Gladman and Picketing 4 pursued this line
of development and provided the following quantitative relationship for yield
strength, tensile strength and impact transition temperature:

YS (N/mm 2) = 53.9 + 32.3% Mn + 83.2% Si + 354% Nf + 17.4d-~

t

TS (N/mm 2) = 294 + 27.7% Mn + 83.2% Si + 3.85% pearlite + 7.7d-~

1

ITT (*C) = -19 + 44% Si + 700~/(%Nf) + 2.2% pearlite - 11.5d-~

where d is the mean ferrite grain size in mm and Nf the free (soluble) nitrogen.